The invention relates to electrical interconnection devices and to methods of making these electrical interconnection devices. More particularly, the invention relates to electrical interconnection devices comprising multiple polymeric and metallic layers which are useful in electronic applications.
The general trend in microelectronic circuits is toward systems of materials which deliver higher performance at a reduced cost. In integrated circuits, the interconnection structure is often the performance limiting and space consuming part of the overall circuit. Recently, multichip modules for interconnecting multiple chips in high density circuits have gained increased interest.
High density, thin film multichip module packaging is one of the more promising techniques among various multichip module packaging approaches because of its fine dimensional capability, use of lower dielectric constant polymers for dielectric interface layers, and ease of processing. The multichips are usually in the form of a multilayered structure, wherein conductive metal layers are separated by an organic dielectric interface layer material. It has been found that certain organic dielectrics offer the potential for achieving higher performance and increased density, and are therefore suitable for use in electronic applications.
The thermomechanical properties of dielectric materials are important for the integrity and reliability of the final circuit. High thermal stability and a reasonably low thermal expansion coefficient are desirable for circuit processing and performance. In multichip modules applications, for example, stability at about 300.degree. C. is considered sufficient for the fabrication process. Silicon-based integrated circuit technologies require somewhat higher processing temperatures, usually exceeding about 400.degree. C. The thermal stability of organic dielectric materials determines the maximum temperature to which the circuit may be exposed during processing and use.
Polyimides have been widely used as the dielectric material despite certain disadvantages. For example, they have a relatively high dielectric constant and high water absorption compared to other polymers. Therefore, for improved reliability and faster signal propagation, polymers with lower water absorption and lower dielectric constant are required. The cyclobutarenes, specifically benzocyclobutanes (BCBs), meet the requirements of lower water absorption and lower dielectric constant and present further advantages. For example, cyclobutarenes have a high degree of planarization and good thermal stability compared to other polymers used in the microelectronic industry. Therefore, cyclobutarenes are currently preferred for microelectronic applications.
The cyclobutarenes in the form of thin films are especially desirable dielectric materials due to their thermal and electrical properties. However, when polymers are formed as thin films on substrates, another critical problem arises: unacceptably low adhesion at the interface between the film and the next adjacent layer, usually a conductive metal layer.
To promote reliable adhesion of a cyclobutarene polymer to an inorganic substrate, one may use an adhesion promoter. In the case of a plastic material, the adhesion promoter may be mixed with the monomer or prepolymer as it is coated on a surface or may be used to coat the surface prior to coating with the cyclobutarene.
Additionally, successive layers of polymer may be efficiently adhered to one another by only partially curing the polymer layers until all layers have been applied. Then by more completely curing the polymer, the contacting layers form chemical bonds between themselves.
Use of adhesion promoters such as those discussed above or partially curing the polymer, does not apply when a conductive metal layer is to be placed over a polymer surface. It is, however, well-known that the adhesion between a polymeric cyclobutarene and metallic material is generally poor.
In view of this deficiency, numerous efforts toward enhancing the adhesion of a metal layer to a polymeric layer have been made. One technique includes depositing an adhesion enhancing metal interface layer (herein also referred to as "tie layer") and then depositing the desired metal layer. Such technique involves pretreating the polymeric surface by backsputtering, either with plasma or reactive ions, usually with high energy density. However, this treatment often disrupts the polymeric layer so severely that diffusion of the tie layer metal into the disrupted polymeric surface may occur, which, in turn, may reduce the performance of the dielectric layer to unacceptable levels. Also, the resulting tie layer often has a thickness between about 200 to about 1000 Angstroms (A), and can decrease the high frequency conductivity of the conductive metal layers.
Therefore, it would be most desirable to provide an electrical interconnection device which has a multilayered structure comprising conductive metal layers separated by a dielectric cyclobutarene polymer layer wherein the conductive metal layers adhere sufficiently to the dielectric layer to withstand processing conditions normally employed in making such devices.